Validation of a Diagnostic Test for Glucose-6-phosphate Dehydrogenase (G6PD) Deficiency in Anti-coagulated Blood

Validation of a Diagnostic Test for Glucose-6-phosphate Dehydrogenase (G6PD) Deficiency in Anti-coagulated Blood

Validation of a Diagnostic Test for Glucose-6-phosphate Dehydrogenase Deficiency: Diagnostic Accuracy and Repeatability in Capillary Samples

The primary objective of the study is to assess the accuracy of the SD Biosensor STANDARD™ point-of-care (POC) G6PD test in measuring G6PD activity and classifying results compared to a reference assay and across repeated measurements in capillary samples.

Cross-sectional diagnostic accuracy study with 250 volunteer participants. The clinic will recruit and consent adult study participants. Clinic staff will draw venous blood and obtain finger stick capillary blood samples. Clinic staff will perform the investigational SD Biosensor STANDARD™ G6PD test for glucose-6-phosphate dehydrogenase (G6PD) deficiency and a HemoCue® hemoglobin test on finger stick capillary blood. An anti-coagulated venous blood sample will be sent to a Clinical Laboratory Improvement Amendments (CLIA) certified lab for G6PD reference testing by the gold standard assays: G6PD measurement by spectrophotometry using the Pointe Scientific G6PD reference assay and hemoglobin measurement by a hematology analyzer. Individuals identified as G6PD deficient or intermediate by the reference test will be notified of their results by the clinic and referred to their physician for follow-up. This study includes a nested repeatability study and a nested sample stability study. In the nested repeatability study up to 20 consented participants will provide 4 additional finger stick samples. Clinic staff will perform the SD Biosensor STANDARD™ G6PD test to assess the repeatability of the test in capillary blood over 8 G6PD and hemoglobin measurements on up to 3 different instruments. In the nested sample stability study up to 8 consented participants will provide an additional venous blood draw sample to be tested at additional time points to document stability of the samples over time when tested by the SD Biosensor STANDARD™ G6PD Test.

Participants provided whole blood samples as well as fingerstick capillary blood samples. At the clinic site lab, study staff conducted the SD Biosensor STANDARD point-of-care G6PD test and the point-of-care HemoCue hemoglobin test on both finger stick blood and whole blood samples. At the reference laboratory, G6PD activity was measured from whole blood samples using the Pointe Scientific G6PD reference assay and hemoglobin was measured using a hematology analyzer.

The SD Biosensor G6PD Analyzer is designed to measure the quantitative determination of total hemoglobin concentration and G6PD enzymatic activity in fresh human whole blood specimens based on reflectometry assays in a point-of-care setting. The test is intended to aid in the identification of people with G6PD deficiency. The test is currently not licensed for use in the US and is considered an investigational product.

The Pointe Scientific test kit will serve as the reference assay to assess G6PD activity. Its intended use is for the quantitative, kinetic determination of G6PD in blood at 340 nm.

The HemoCue hemoglobin (Hb) 201+ system is designed for quantitative point-of-care whole blood hemoglobin determination in primary care using a specially designed analyzer, the HemoCue Hb 201+ Analyzer, and specially designed microcuvettes, the HemoCue Hb 201+Microcuvettes.

For the purposes of this study, an individual was considered G6PD deficient if they tested positive in the Pointe Scientific assay. A true positive was defined as a participant with ≤ 30% of normal G6PD activity in circulating venous blood determined by the Pointe Scientific test. Diagnostic sensitivity of the SD Biosensor STANDARD G6PD test is defined as the percentage of participants who tested positive for G6PD deficiency on the reference test who were identified by the test assay as positive, calculated as: Number of participants who were both test and true positive / (Number of participants who were test and true positive + Number of participants who were test negative but true positive [ie false negative]) * 100%. Sensitivity of the SD Biosensor STANDARD G6PD test was calculated from both venous and capillary blood samples.

To investigate the performance of the SD Biosensor STANDARD G6PD test to distinguish females with intermediate G6PD activity from females with normal activity, assay sensitivity was determined at a G6PD activity threshold of 70%. A true positive for intermediate G6PD activity in females was defined as G6PD activity between 30 and 70% of normal in circulating venous blood as determined by the Pointe Scientific test. Sensitivity of the SD Biosensor STANDARD G6PD test is the percentage of women who tested positive for intermediate G6PD activity on the reference test who were identified by the test assay as positive, calculated as: Number of women who were both test and true positive / (Number of women who were test and true positive + Number of women who were test negative but true positive [ie false negative]) * 100%. Sensitivity of the SD Biosensor STANDARD G6PD test for identifying females with intermediate G6PD activity was calculated from both venous and capillary blood samples.

For the purposes of this study, an individual was considered G6PD deficient if they tested positive by the Pointe Scientific assay. A true negative was defined as > 30% of normal G6PD activity in circulating venous blood as determined by the Pointe Scientific test. Specificity is the percentage of participants who tested negative for G6PD deficiency on the reference test who were identified as negative using the test assay, calculated as: Number of participants who were both test and true negative / (Number of participants who were test and true negative + Number of participants who were test positive but true negative [ie false positive]) * 100%. Specificity of the SD Biosensor STANDARD G6PD test was calculated from both venous and capillary blood samples.

To investigate the performance of the SD Biosensor STANDARD G6PD test to distinguish females with intermediate G6PD activity from females with normal activity, the specificity was determined at a G6PD activity threshold of 70%. A true negative for intermediate G6PD activity in females was defined as G6PD activity > 70% of normal in circulating venous blood as determined by the Pointe Scientific test. Specificity is the percentage of participants who tested negative for G6PD deficiency on the reference test who were identified as negative using the test assay, calculated as: Number of participants who were both test and true negative / (Number of participants who were test and true negative + Number of participants who were test positive but true negative [ie false positive]) * 100%. Specificity of the SD Biosensor STANDARD G6PD test was calculated from both venous and capillary blood samples.

Accuracy between the SD Biosensor STANDARD G6PD test assay and the Pointe Scientific G6PD reference assay was calculated as the percent agreement between both G6PD tests, ie, the percentage of participants with the same diagnosis according to both tests (either deficient, intermediate, or normal G6PD levels). Accuracy of the SD Biosensor STANDARD G6PD test was calculated from both venous and capillary blood samples.

Accuracy Between the SD Biosensor STANDARD G6PD Test Measure of Hemoglobin and the Reference Hemoglobin Test

Accuracy between the SD Biosensor STANDARD G6PD test measure of hemoglobin and the hemoglobin reference assay was calculated as the percentage agreement between both tests, ie, the percentage of participants with the same diagnosis according to both tests (either non/mild anemia, moderate anemia or severe anemia).

Repeatability Substudy: G6PD Levels in Capillary Blood Samples Measured Using the SD Biosensor G6PD Test, by Operator and Analyzer

Capillary blood samples were collected in duplicate from four different fingers on the participants hands, for a total of eight samples. Within each duplicate, a sample was tested on 1 of 2 SD Biosensor G6PD instruments by 1 of 2 operators. Overall there were 3 instruments used in the testing and 3 operators.

Repeatability Substudy: Hemoglobin Levels in Capillary Blood Samples Measured Using the SD Biosensor STANDARD Hemoglobin Test, by Operator and Analyzer

Capillary blood samples were collected in duplicate from four different fingers on the participants hands, for a total of eight samples. Within each duplicate, a sample was tested on 1 of 2 SD Biosensor instruments by 1 of 2 operators. Overall there were 3 instruments used in the testing and 3 operators.

Each participant in the sample stability substudy underwent an additional blood draw in 3 different anti-coagulants which were stored at room temperature (15-30°C/59-86°F). The freshly collected venous whole blood samples were tested at the clinic site lab using the SD Biosensor STANDARD G6PD test within 1 hour of collection for baseline (0 hour) and at 4 additional time points, up to 2 days (48 hours) after collection. The anti-coagulants included: ethylenediaminetetraacetic acid (EDTA)-anti-coagulated blood heparin-anti-coagulated blood acid citrate dextrose (ACD)-anti-coagulated blood

Blood samples were collected on day 1. Samples were tested immediately (< 1 hour) and at 2, 4, 6, and 24 hours after collection.

Each participant in the sample stability substudy underwent an additional blood draw in 3 different anti-coagulants which were stored in a refrigerator (2-8°C/25-46°F). The freshly collected venous whole blood samples were tested at the clinic site lab using the SD Biosensor STANDARD G6PD test within 1 hour of collection for baseline (0 hour) and at 5 additional time points, up to 7 days (168 hours) after collection. The anti-coagulants included: ethylenediaminetetraacetic acid (EDTA)-anti-coagulated blood heparin-anti-coagulated blood acid citrate dextrose (ACD)-anti-coagulated blood

Blood samples were collected on day 1. Samples were tested immediately (< 1 hour) and at 24, 48, 72, 96, and 168 hours after collection.

Each participant in the sample stability substudy underwent a blood draw in 3 different anti-coagulants which were stored at room temperature (15-30°C/59-86°F). Hemoglobin levels were measured from the freshly collected venous whole blood samples at the clinic site lab using the SD Biosensor STANDARD hemoglobin test within 1 hour of collection for baseline (0 hour) and at 4 additional time points, up to 24 hours after collection. The anti-coagulants included: ethylenediaminetetraacetic acid (EDTA)-anti-coagulated blood heparin-anti-coagulated blood acid citrate dextrose (ACD)-anti-coagulated blood

Blood samples were collected on day 1. Samples were tested immediately (< 1 hour) and at 2, 4, 6, and 24 hours after collection.

Each participant in the sample stability substudy underwent an additional blood draw in 3 different anti-coagulants which were stored in a refrigerator (2-8°C/25-46°F). Hemoglobin levels were measured from the freshly collected venous whole blood samples at the clinic site lab using the SD Biosensor STANDARD hemoglobin test within 1 hour of collection for baseline (0 hour) and at 5 additional time points, up to 7 days (168 hours) after collection. The anti-coagulants included: ethylenediaminetetraacetic acid (EDTA)-anti-coagulated blood heparin-anti-coagulated blood acid citrate dextrose (ACD)-anti-coagulated blood

Blood samples were collected on day 1. Samples were tested immediately (< 1 hour) and at 24, 48, 72, 96, and 168 hours after collection.

Inclusion Criteria: Must communicate an understanding of the study protocol. Must be able to provide written consent to undergo screening and provide medical history. Participants must be afebrile and in general good health in the opinion of the investigator as determined by vital signs, medical history, and physical examination. Black/African-American, by self-report. Exclusion Criteria: Blood transfusion in the past 3 months by self-report

Pal S, Myburgh J, Bansil P, Hann A, Robertson L, Gerth-Guyette E, Ambler G, Bizilj G, Kahn M, Zobrist S, Manis MR, Styke NA, Allan V, Ansbro R, Akingbade T, Bryan A, Murphy SC, Kublin JG, Layton M, Domingo GJ. Reference and point-of-care testing for G6PD deficiency: Blood disorder interference, contrived specimens, and fingerstick equivalence and precision. PLoS One. 2021 Sep 20;16(9):e0257560. doi: 10.1371/journal.pone.0257560. eCollection 2021.